Code review request: 8002273 NMT to report JNI memory leaks when -Xcheck:jni is on

David Holmes david.holmes at
Thu Nov 8 20:06:19 PST 2012

Hi Zhengyu,

On 9/11/2012 3:23 AM, Zhengyu Gu wrote:
> This fix is related to JDK-8001743: Overlapped thread stacks. The cause
> of 8001743 is that, an attached JNI thread exited without detaching the
> thread, so JVM will leak a JavaThread object that attached to the JNI
> thread.
> The patch allows NMT to report such case when -Xcheck:jni VM option is
> specified.

I'm a little unclear who is doing the checking here. Is it the case that 
a regular thread while updating its NMT records, detects that there is 
an overlap with an existing region, and infers from that that the other 
region must belong to a thread that failed to detach?

This comment doesn't read clearly to me, and we don't generally include 
references to bug reports:

  138   // an attached JNI thread can exit without detaching the thread, 
that results
  139   // JVM to leak JavaThread object (JDK-8001743)

If my understanding of the check is correct then to me a clearer comment 
would be:

// Overlapping stack regions indicate that a JNI thread failed to
// detach from the VM before exiting. This leaks the JavaThread object.


> Thanks,
> -Zhengyu

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